1. Field of the Invention
The present invention relates to cooling apparatuses for controlling temperature rises in heat generating parts in electrical equipment, and more particularly to a heat sink assembly having combined fins for dissipating heat generated by an electrical package such as a Central Processing Unit (CPU).
2. Prior Art
During operation of a computer, heat is generated by the electrical components thereof, and especially by electronic packages such as central processing units (CPUs). High-speed processing of signals by a CPU results in a correspondingly high amount of heat being generated. Thus, cooling of CPUs is an important consideration in designing computers.
Referring to FIG. 4, U.S. Pat. No. 4,884,331 discloses an aluminum-extruded heat sink 10 having a comb-shaped cross section. The heat sink 10 comprises a base, and a plurality of cooling pins extending from the base. Heat is first conducted to the base and then to the cooling pins, whereupon the heat is radiated to ambient air. Because heat radiation mainly occurs at the surfaces of the cooling pins, a large total surface area of the cooling pins is required when configuring the heat sink. This can be obtained by configuring more cooling pins on the base, or by providing elongated cooling pins. However, a thickness and a height of the cooling pins are limited due to inherent restrictions in the relevant fabrication processes. In the case of fabrication by extrusion, the maximum attainable ratio of the height h of each pin and the distance d between two adjacent pins is approximately 13 to 1. This limits the total surface area of the cooling pins per unit area of the base of the heat sink 10.
In order to obtain a larger heat-radiating surface area, heat sinks having a plurality of jointed plates or fins have been developed. Referring to FIG. 5, one such heat sink 30 comprises a plurality of plates 32 having top and bottom flanges 34. Each top and bottom flange 34 defines a pair of locking slots 36 near opposite ends thereof, and comprises a pair of insertion tabs 38 extending from adjacent the locking slots 36. Each insertion tab 38 forms a bulge 39 on a top side thereof, and defines a recess in an underside thereof. In assembly, the insertion tabs 38 of a rear one of the plates 32 are inserted into the locking slots 36 of an adjacent front one of the plates 32. The bulges 39 of the insertion tabs 38 of the rear plate 32 are engaged in the recesses of the insertion tabs 38 of the front plate 32, so that the rear plate 32 is connected to the front plate 32. Other plates 32 are attached to the combined rear and front plates 32 in the same way.
However, the locking slots 36 and the insertion tabs 38 are formed on a periphery of a main body of each plate 32. When the plates 32 are made very large in order to provide large heat radiating surfaces, the center portions of the main bodies of the plates 32 are liable to easily deform. When this happens, the passage for air flow between adjacent plates 32 is narrowed, or may even be blocked altogether. In addition, the engagement between the bulges 39 and the recesses is unstable. The heat sink assembly 30 is prone to be split apart when subjected to shock or vibration during transportation or use.